3D-printed Rectangular-to-circular Waveguide Mode Converters: Design, Fabrication and Experimental Validation at X-band

This paper presents the design, simulation, fabrication, and experimental validation of 3D-printed WR90 rectangular-to-circular waveguide mode converters operating at 10 GHz. The manufacturing approach enables rapid prototyping of complex transition geometries, transforming electromagnetic waves from a standard rectangular waveguide (22.86 × 10.16 mm) to a circular waveguide (radius 11.9125 mm) through a linear transition profile. This profile enables a gradual mode transformation from TE₁₀ to TE₁₁ modes. Two fabrication approaches are investigated: 3D printing with conductive paint metallization and direct metal 3D printing. Electromagnetic simulations using CST Microwave Studio predict return loss S₁₁ better than −30 dB across 8-12 GHz. Experimental characterization shows S₁₁ minima of −20 dB (plastic) and −18 dB (metal) at 10 GHz, with S₁₁ better than −15 dB maintained across 9-11 GHz (VSWR < 1.43). Plastic printing with metallization yields approximately $35 per unit and 3-4 hours fabrication, whereas direct metal printing yields approximately $180 per unit and 5-6 hours. Both approaches offer substantial cost and lead-time advantages over conventional machining.